Not a tammy expert(raisinhall or lill will know best) but she looks fine to me especially for 6yrs old. Only 2lb of food a day sounds stingy to me as all my stock(GOS) including the old farts are on 1kg am & 1kg pm and thats me cutting them back

(recalibrated measuring scoop) this explains why she's grazing, pigs don't really get much sustinencce from grass but its a good tummy filler so chances are she's a bit hungry. Go by eye is my best advice, if she seems happy enough go with your current regime, feeling for her backbone is usually a good guide, it should be feelable thro a layer of good fat, if you can't feel it she's too fat and if it sticks out like a skeleton she's too thin. Go with your gut instinct.
Don't worry about being a softie and keeping her as a pet, i still have an 8yr old boar, deaf, fires blanks, as cantankerous and as stubborn as they come but God love 'im he's still here!

(and i don't mean OH!)
HTh mandy